#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define DEFAULTLENGTH 20

char *genrkey(int);

int main(int argc, char *argv[]) {
  int len;
  char *key;

  if (argc < 2) len = DEFAULTLENGTH;
  else len = atoi(argv[1]);

  key = genrkey(len);
  printf("%s\n", key);
  free(key);

  return 0;
}

char *genrkey(int len) {
  int i;
  char *buffer = malloc(len+1), _bank[62] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  FILE *rand;

  memset(buffer, 0, len);
  if ((rand = fopen("/dev/urandom", "r")) != NULL) {
    for (i=0; i<len; i++)
      buffer[i] = _bank[fgetc(rand)%62];
    buffer[len] = 0;
  }

  return buffer;
}